The present invention relates to a method for disassembling two ultrasonically welded elements as well as an element that can be ultrasonically welded to another element making it possible to implement said method. The invention is more particularly suitable for separating a holder or part of a holder ultrasonically welded to a wall.
According to one known embodiment illustrated in FIGS. 1 to 3, a holder 10 comprises a body 12, in the form of a cylindrical pellet with a front surface 14, that can be pressed against and connected to a wall 16 of an aircraft. The body 12 is extended by a rod 18 that makes it possible to connect a “light” element, in particular less than 2 kg, to the structure of the aircraft, for example such as an electrical cable, a tube, an insulating pad, cabin furniture, etc.
The holder 10 is made from a composite material, for example thermoplastic resin, which may or may not be reinforced with fibers.
The wall 16 of the aircraft is also made from a composite material, and for example comprises fibers embedded in a thermosetting resin matrix. According to the embodiment illustrated in FIGS. 2 and 3, the wall 16 comprises a coating 20 made from a thermoplastic material. Advantageously, the structure of the wall and its coating are co-polymerized, which makes it possible to obtain a solid connection between the coating and the wall.
As illustrated in FIG. 3, the holder 10 is fastened to the wall 16 using an ultrasonic welding method.
According to this technique, the holder is in contact with a vibration transmitter and its front surface 14 is pressed against the wall. Subsequently, by applying vibrations, heat is created at the interface between the holder and the wall up to their melting temperatures, allowing the molecular chains of the two elements in contact to mix in a diffusion area 22. After the vibrations have stopped and cooling has taken place, a solid junction is obtained.
To concentrate the heating, the front surface of the holder comprises at least one protruding shape called an energy director 24. As illustrated in FIG. 1, an energy director describes a ring approximately concentric to the body of the holder with a triangular section and a height in the vicinity of 1.5 mm. After the vibrations have stopped, the energy director 24 is deformed and forms a junction 26 between the holder and the wall, as illustrated in FIG. 3.
This assembly technique is in particular described in documents EP-2.004.388 and EP-1.423.256.
Following such an assembly, it may be necessary to reinstall a holder, for example if it is broken or due to a defective initial assembly. However, ultrasonic welding is a practically irreversible assembly technique. It is particularly irreversible inasmuch as the energy director(s) do not have the same geometry as before the assembly, and no longer have a pointed shape making it possible to concentrate the vibrational energy.
To disassemble the holder, a first solution consists of using a cutting and heating tool such as a blade and sliding it between the holder and the wall so as to destroy the junction 26. This solution is not fully satisfactory, as the risks of damaging the wall made from the composite material are high due to the geometry of the blade-shaped tool and the heat produced by the latter.
Another solution consists of using an ultrasonic knife, which is inserted between the holder and the wall in order to destroy the junction 26. As before, this solution is not fully satisfactory, as the risks of damaging the composite material wall are high.
Another solution consists of cutting out the holder using a rotating tool. This rotating tool has a cylindrical shape with at least one cutting edge at a front surface and an opening to allow the passage of the rod 18 of the holder, which may be used as axis of rotation. This tool also comprises two radial handles allowing it to be maneuvered.
This rotating tool makes it possible, through machining such as end milling, to remove material and thereby eliminate the holder.
Unlike the first two solutions, this solution makes it possible to limit the risks of damage to the wall. However, the surface of the wall may be scratched after this disassembly operation.
Document U.S. Pat. No. 5,591,364 proposes positioning a wire near the junction formed ultrasonically, then circulating an electric current in the wire so as to cause heating by Joule effect in order to cause the junction to soften. According to this document, the wire is stationary. As before, this solution is not fully satisfactory, as the risks of damage to the composite material wall are high due to the heating caused by the wire. Furthermore, the solution is not easy to implement inasmuch as it is difficult to position the wire correctly relative to the junction.